Okay, we are given 7920205959 and 5550337979. Let's add them up step by step.

Step 1: We'll start by adding the digits 9 & 9 in column 1 and get 18.
We'll write down the last digit 8 and carry the 1 to the next column.

Step 2: We'll start by adding the digits 5 & 7 in column 2 and get 13.
We'll write down the last digit 3 and carry the 1 to the next column.

Step 3: We'll start by adding the digits 9 & 9 in column 3 and get 19.
We'll write down the last digit 9 and carry the 1 to the next column.

Step 4: We'll start by adding the digits 5 & 7 in column 4 and get 13.
We'll write down the last digit 3 and carry the 1 to the next column.

Step 5: We'll start by adding the digits 0 & 3 in column 5 and get 4.

Step 6: We'll start by adding the digits 2 & 3 in column 6 and get 5.

Step 7: We'll start by adding the digits 0 & 0 in column 7 and get 0.

Step 8: We'll start by adding the digits 2 & 5 in column 8 and get 7.

Step 9: We'll start by adding the digits 9 & 5 in column 9 and get 14.
We'll write down the last digit 4 and carry the 1 to the next column.

Step 10: We'll start by adding the digits 7 & 5 in column 10 and get 13.
We'll write down the last digit 3 and carry the 1 to the next column.

So, 7920205959 + 5550337979 = 13470543938.

